The long-term objective of this project is to investigate technical and analytic means of identifying from the body surface low-level signals arising from the conduction system of the heart. Our hypothesis is that such signals, (previously considered too weak, or too noise-contaminated for surface recognition) are accessible on the surface and contain the essential diagnostic information now consistently obtainable only by cardiac catheterization or open-chest techniques. Our approach is two-pronged: (1) progressive discovery and refinement of technical means of noise reduction and signal amplification using specially designed amplifiers, logic-circuitry, filters and electrodes and (2) utilization of multiple-lead body surface mapping techniques with appropriate computer software development in order to analytically identify and describe the His-Purkinje signal in terms of its frequency content, multipolar generator content, its pathway through the conduction system, and the body sites of greatest sensitivity. A computer model of the sino-ventricular conduction system will be completed and be expected to give insight into the interpretation of the biologic data. Eventually, if data from the His-Purkinje system can be obtained with ease just as the clinical electrocardiogram, not only will society be benefited from the health standpoint and the economic standpoint, but the field of research into problems of cardiovascular diagnosis, cardiac conduction, abnormal rhythms, antiarrhythmic drug testing, and studies of the mechanism of the genesis of arrhythmias will be enhanced.